The present invention relates to a non-perfluoro fluorine-containing resin molded article having a heat-sealing property at low temperature and a high adhesive strength, particularly to a cover film for solar batteries.
Since fluorine-containing resins have excellent non-sticking property, fluorine-containing resin molded articles cannot be jointed with each other or with a different material only by using an adhesive.
Also for joining the fluorine-containing resin molded articles with each other, high frequency welding and ultrasonic wave welding which are usually used in processing general-purpose resins cannot be employed because parts to be jointed cannot be melted again. Accordingly with respect to heat-meltable fluorine-containing resins, so-called melt adhesion method, in which the resin is subjected to heating at a temperature of not less than a melting point thereof and then pressing in a re-molten state, has been used. However in the melt adhesion method, since the fluorine-containing resin molded article is once melted, a mechanical strength thereof around a jointed part is lowered remarkably.
On the other hand, when the fluorine-containing resin molded article is jointed with a different kind of material, there is a chemically treating method, in which a surface of the fluorine-containing resin molded article is chemically modified with sodium-naphthalene and then joining is carried out by using an adhesive. However the method has a problem with coloring of the molded article and therefore cannot be used for applications where transparency is required.
To solve the above-mentioned problems, there are various proposals for discharge-treatment of a surface of the molded article.
For example, there are the following known methods.
(1) A method of low temperature plasma treatment by glow discharging of a molded article of perfluoro fluorine-containing resin such as polytetrafluoroethylene, tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer or tetrafluoroethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether) copolymer having a ratio of the number of fluorine atoms to the number of carbon atoms (hereinafter referred to as xe2x80x9cF/Cxe2x80x9d) of 1.8 to 2.0 to decrease F/C on the surface of molded article to 0.5 to 1.75 and then heat-sealing at a temperature of about 210xc2x0 C. without using an adhesive (JP-B-5-68496),
(2) A method of low temperature plasma treatment by glow discharging of a molded article of perfluoro fluorine-containing resin having a ratio F/C of the number of fluorine atoms to the number of carbon atoms of 1.9 to 2.0 in non-polymerizable gas atmosphere having an oxygen content of not more than 10% by mole to decrease F/C of the surface of molded article to 0.8 to 1.8 and to adjust a ratio of the number of oxygen atoms to the number of carbon atoms (hereinafter referred to as xe2x80x9cO/Cxe2x80x9d) to not more than (0.2-0.09xc3x97(F/C)) and then heat-sealing at a temperature of about 210xc2x0 C. without using an adhesive (JP-B-2-54848),
(3) A method of discharge treatment of a surface of molded article of perfluoro fluorine-containing resin in a stream of an organic compound having functional group (for example, ketone and acrylic acid monomer) to impart a heat-sealing property to the surface (JP-B-37-17485, JP-B-49-12900, U.S. Pat. No.3,296,011),
(4) A method of continuous plasma treatment of a surface of a sheet in a chamber charged with helium gas or a gas mixture mainly comprising helium gas (JP-A-3-143930), or a method of imparting a hydrophilic property to plastic and fiber by glow discharging at atmospheric pressure in a stream with steam of a rare gas or gas mixture of rare gas and ketone (JP-A-6-182195),
(5) A method of modifying a surface of perfluoro or non-perfluoro fluorine-containing resin molded article by discharge treatment such as corona discharging, glow discharging and plasma discharging in an inert gas atmosphere containing an organic compound having functional group (for example, acetone, glycidyl methacrylate, methanol, or the like) and then jointing by using an adhesive having functional group having affinity to a functional group of the organic compound (Japanese Patent No.2690032), and the like method.
However the above-mentioned methods (1) to (3) are directed to only perfluoro fluorine-containing resin molded articles, and treatment under reduced pressure is required.
In the method (4), since the fluorine-containing resin film is passed between the parallel plate type electrodes, the both sides of the film is treated, thus greatly lowering non-sticking property, water repellency, lubricity, stain-proofing property and chemical resistance which are features of the fluorine-containing resin. In order to make the best use of such features of the fluorine-containing resin, an opposite side of the film which is not treated must be covered with a protection film. Further in the method described in JP-A-6-182195, since an inert gas or fluorocarbon is used, the treating system must be made air-tight and collection of exhaust gas has to be considered.
The method (5) is featured by coating an adhesive having a functional group having a specific relation to the organic compound used as an atmosphere.
As mentioned above, improvements have been made mainly in heat-sealing property of perfluoro fluorine-containing resin molded articles having F/C exceeding 1.8. However a heat-sealing property of non-perfluoro fluorine-containing resins having F/C of not more than 1.8 is not enhanced as compared with perfluoro fluorine-containing resins only in case of the same treatment as in perfluoro fluorine-containing resins, and in many cases, an adhesive is necessary.
An object of the present invention is to impart excellent low temperature heat-sealing property to a surface of molded article of non-perfluoro fluorine-containing resin having F/C of not more than 1.8.
The present invention relates to a non-perfluoro fluorine-containing resin molded article, particularly a molded article in the form of film having a surface layer portion having a low temperature heat sealing property on at least a part of the surface layer thereof, in which a ratio F/C of the surface layer portion having a low temperature heat-sealing property is 0.2xe2x89xa6F/Cxe2x89xa60.9, preferably 0.3xe2x89xa6F/Cxe2x89xa60.8, particularly preferably 0.4xe2x89xa6F/Cxe2x89xa60.8 and a ratio O/C thereof is 0.09xe2x89xa6O/Cxe2x89xa60.40, preferably 0.14xe2x89xa6O/Cxe2x89xa60.30, particularly preferably 0.14xe2x89xa6O/Cxe2x89xa60.25, and a ratio F/C of the remaining portion of the surface layer is larger than that of the surface layer portion having a low temperature heat-sealing property and is 0.8xe2x89xa6F/Cxe2x89xa61.8.
The molded article in the form of film is suitable as a cover film for solar batteries, in which one side of the film has a surface layer portion having a low temperature heat-sealing property and a high heat-sealing strength. The molded article can also be used as a laminated article for covering of solar batteries by heat-sealing directly to an ethylene/vinyl acetate film or sheet at a temperature less than a melting point of the non-perfluoro fluorine-containing resin.